1. Field of the Invention
A new improved catalyst system for alpha-olefin type polymerizations includes a metal alkyl cocatalyst having the formula T.sub.n MR'.sub.3-n in combination with a Group IVB-VIII transition metal compound on a support and a Lewis base wherein n is equal to one or two, T is equal to R.sub.3 DCH.sub.2, and wherein D is selected from the group consisting of Si, Ge or Sn, R is methyl or ethyl, and R' is selected from the group consisting of C.sub.1 to C.sub.8 primary alkyl or aralkyl groups including unhindered branched groups and M is selected from the group consisting of aluminum, gallium or indium. The improved catalyst system provides both increased polymerization activity and polymers having a high degree of isotactic stereoregularity as well as lower catalyst residue.
2. Description of the Prior Art
There is extensive art on the polymerization of ethylene and higher alpha-olefins, including dienes, using Ziegler type catalysts containing either alkyl metals or alkyl metals in which an alkyl group has been replaced by X, OR, SR, NR.sub.2, etc., in combination with a transition metal compound of Groups IVB-VIII, where X=halide, and R=C.sub.1 to C.sub.20 hydrocarbyl substituent.
It is well known to use various alkyl aluminum compounds in combination with transition metal compounds of Groups IVB-VIII in Ziegler-type polymerizations of alpha-olefins. For stereospecific polymerization of propylene and higher alpha-olefins, the most effective commercially used alkyl metal compounds used commercially are AlEt.sub.3 and AlEt.sub.2 Cl, although Al(n-Pr).sub.3, Al(n-Bu).sub.3, Al(i-Bu).sub.3 and Al(iBu).sub.2 H give similar results. Longer chain alkyl aluminums, such as Al(n-C.sub.6).sub.3, Al(n-C.sub.8).sub.3, (n-C.sub.8).sub.2 AlCl, etc., drastically reduce stereospecificity as shown by much lower heptane insolubles.
This invention claims novel, improved alkyl metal cocatalysts for use with Groups IVB-VIII transition metal compounds for stereospecific polymerization of propylene and higher alpha-olefins. The new cocatalysts are di- or tri-organo metal compounds of aluminum, gallium or indium which contain at least one R.sub.3 SiCH.sub.2, R.sub.3 GeCH.sub.2 or R.sub.3 SnCH.sub.2 group. These cocatalysts having bulky groups yield higher activity and isospecificity than the conventional primary di- or trialkyl metal compounds when used in combination with the various types of transition metal catalysts, such as MgCl.sub.2 -supported TiCl.sub.4, TiCl.sub.3.xAlCl.sub.3, low aluminum, high surface area TiCl.sub.3, etc., with or without other catalyst modifiers present, such as Lewis bases, alcohols, phenols, polymers, dispersants, binders and other additives.
A number of U.S. Patents have been issued on the use of tri- or dialkyl organo metal compounds as catalyst for the polymerizations of various C.sub.3 and higher alpha-olefins. However, these patents fail to teach, imply or infer the inventive concept of having at least one bulky R.sub.3 D groups in the tri- or dialkyl organo metal compound in order to be able to simultaneously achieve both increased polymerization activity and improved isotacticity of the resultant polymer. These U.S. Pat. Nos. are: 3,953,414; 3,888,789; 3,992,322; Belgium Pat. No. 845,593 and British Pat. No. 1,335,887.